How soon must we bring a lawsuit on behalf of our child?

In Washington the time to bring a lawsuit is usually 3 years from the date of loss.  This time period is called the statute of limitations.  For children however, the statute of limitations is tolled until the child's 18th birthday.  That means the child can bring a lawsuit up until the child's 21st birthday.  However, it is usually not recommended that the child wait this long to settle the claim or file suit.  Each case is different however, so you should consult with counsel about the best time to conclude the claim or file a lawsuit.